Pickup info

[Georg]

Ed,

Mainly for position sensing but also for string-vibration sensing ... what distance-range does the chip (in your circuit) cover?

I have this idea of attaching a slightly flexible metal-cover onto a floating neck on top of a frame holding the mechanics, and intend to "tune" the cover a bit while playing - using my underarms to push on what would normally be the padded area. Would be nice if I could not only tune the PSG's "body-tone" a little this way, but also affect stages in the built-in electronic sound-chain by pushing on the "pad" in various ways.

By measuring the distance-variation between metal-cover and frame at a few points, I may end up with a real-time "tone-machine" that can slide in and out of preset effects and even switch between effects. I thought of using optocouplers here, but your circuit may work just as well if the distance-range suits my construction.

[ed packard]

Georg;

Look up the HONEYWELL HMC1501 series for operational info. TYhere are several ways to use it. The DC that I use for position sensing might work for as far as a half inch or more, depending upon what gain is chosen and what activation source. When you get ready, I might send you a channel to mess about with.

For the string pickup, I use AC coupled, and string to chip proximity like the standard pickup.

Edp

[Georg]

Ed,

Thanks. Range etc. looks fine for what I will use it for.

Georg

[richard37066]

Georg -

For lucid explanations of how a device works, I always search out the application notes. Here is a link to the app notes (AN211) for the Honeywell 1501.

http://www51.honeywell.com/aero/common/ ... ensors.pdf

Interesting reading.

Richard

[Georg]

Richard, thanks for the link. Somehow I got it down through my shitty connection.

I know how the device work - my profession from years back. What I have learned the hard way not to trust producer's papers on, is how well it will work in a given circuit under defined conditions, and how close tolerances I can expect components to be within. So, I ask those who have tried and tested a batch under conditions close to what I plan to use them for.

[richard37066]

Georg -

Fortunately, Honeywell does cite a couple of manufacturing tolerances which affect, slightly, the performance of the device. This sort of thing also falls within my expertise in many moons past.

Ed Packard will, no doubt, supply us with the straight and complete skinny such that the "Aha" light bulb burns brightly and we don't have to spend hours at the test bench screwing things together.

In retrospect, my effort at creating essentially the same thing some 35 years ago was monstrous in comparison to Ed's teensy circuit board. Blessed be technology! Since Ed has said that he's going to release his design to the public domain, then I won't hesitate in using it in my instrument.

Richard

[Georg]

Ed Packard will, no doubt, supply us with the straight and complete skinny such that the "Aha" light bulb burns brightly and we don't have to spend hours at the test bench screwing things together.

I love memory-refreshes

[ed packard]

The Honneywell info indicates that the device can resolve magnet position to within a degree, and its unamplified output is about 120mV for plus to minus 45 deg.
Apple computer uses magnets to hold their connectors in place. They needed a way to measure the angle of magnetization in their magnets within a degree. Mypickup/position device provided that (as a consultant). Problem was, as was stated to them beforehand, that the magnet maker could not magnetize to that accuracy.

Surprise...I do NOT need external magnets to make the pickup work. If I did there would be difficulty getting the 60 to 80 db of string isolation to allow individual string resolution.

Edp

[ed packard]

Photos in my previous Forum posts have been regrouped on PHOTOBUCKET. They may not appear in the Forum posts from the past. However, you can go to my PHOTOBUCKET site and prowl around...you might find some things of interest.

Player event photos are here:
http://s75.photobucket.com/albums/i287/ ... %20DECADE/

30+ PSGs analyzed are here:
http://s75.photobucket.com/albums/i287/ ... STRUMENTS/

Pickup design info is here:
http://s75.photobucket.com/albums/i287/ ... 20SENSORS/

Integrated tuner/changer (BEAST) info is here:
http://s75.photobucket.com/albums/i287/ ... 20CHANGER/

Tuning structure info is here:
http://s75.photobucket.com/albums/i287/ ... TRUCTURES/

Zirc bar info is here:
http://s75.photobucket.com/albums/i287/ ... %20OTHERS/

The above info is brought to you by ZIRC BARS...Got ZIRC?

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Available:

White, 7/8 X 3+3/8"
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Thank you for your interest.
Edp

[ed packard]

Further considerations re wire size and type for common wound pickups:

In a quick summation of the electrical properties of wound pickups, we have R as a function of the length and diameter of the wire. The length (and hence the R) will be a function of the number of strings and the spacing of the strings. From this we may reason that a six string pickup for a standard guitar (3/8” string spacing) will have less resistance than a 10 string pickup for a PSG (string spacing of 11/32”), and much less than that for a 14 string PSG.

What size and type of wire do we want to use? The answer is it depends upon what results we want from the pickup. “In the beginning”, there were limits to the available wire size. #44 gauge was considered the upper limit for available wire. Most pickups were wound with #40 single filament, or larger diameter wire.

Today #54 single, and double filament (bifilar) wire is readily available. Check the wire table previously referenced on my Photobucket site and check the Ohms per Kft for #52, and # 36.

Remembering that the R increases linearly with the number of turns, and the L increases as the square of the turns, we can control to a degree the ratio of R to L by changing the number of the turns, and the size of the wire.

Now look at the Inductive Reactance chart on the Photobucket site. Notice how the Inductive Reactance varies with frequency when we increase the inductance (L).

Our PSGs are capable of producing string vibrations from C1 (low string fundamental on the BEAST) to the A4 fundamental on a raised G# on a 10 or 12 string E9 tuning. A4 would be A4=440Hz. If we bar the string at the 12th fret we have A5=880 Hz. Now at the 24th fret we have a fundamental of A6=1660Hz., the second harmonic of which is A7=3320Hz, and the 4th harmonic of which is A8=6640 Hz and so forth. The PSGs are capable of producing string vibrations beyond what the common pickups are capable of capturing. Check these Hz values as I am writing off the top of my little bald head.

It would seem that we would like to keep the L low so that adding the 500K resistive volume pedal, and the amplifier input impedance will not cost the loss of high frequencies…further, we would like to keep the R high so as to lower the Q of the pickup, thus flattening it’s frequency response. The pickup output varies with the number of turns so we need a reasonable number of turns…the tradeoffs are yours to make…but you now have the smaller diameter (#52 & 54 etc.) to wind the pickup with.

We have not said much about C (capacitance). One would expect that it will be a function of wire length, wire size, and winding style. It will be distributed along the winding, and tend to shunt the higher frequencies = we would like to keep the C low. Smaller diameter wire => higher capacitance per foot of wire.

Ignoring the magnetic properties of the pickup for the moment…What would you want the RLC of your pickup to be and why?

You can profile the pickup for impedance vs. frequency by putting a resistor in series with the winding, and driving the pickup thru the resistor with a variable frequency. When the voltage drop across the resistor = the drop across the pickup coil, that is the Z of the pickup at that frequency. You should get a “belly up” curve vs. frequency. Do this to see what an assortment of pickups do to the frequency response curve…now what response do you prefer?

Of course the new semiconductor pickup does not have the problems associated with windings!!!

Next will probably be the “magnetic circuit”.

I can see what the interest level is by the number of hits on the Photobucket site…many seem to have an interest.

Edp